Radiation imaging apparatus, apparatus control method, and computer-readable storage medium storing program for executing control

ABSTRACT

To provide a radiation imaging apparatus which is capable of both connecting state radiographing for radiographing with a C arm connected and non-connecting state radiographing for radiographing with the C arm disconnected, and is convenient and obtains high quality images, the apparatus includes: a flat panel detector; a holding unit for holding at least the flat panel detector; and a control unit for controlling the flat panel detector. With the configuration, the flat panel detector can be connected to and disconnected from the holding unit; connecting state radiographing can be performed with the flat panel detector connected to the holding unit, and non-connecting state radiographing can be performed with the flat panel detector disconnected from the holding unit; the control unit controls the flat panel detector such that a heat generation quantity of the flat panel detector during the non-connecting state radiographing can be lower than a heat generation quantity of the flat panel detector during the connecting state radiographing.

RELATED CASES

This application is a divisional of application Ser. No. 11/692,534,filed Mar. 28, 2007, claims benefit of that application under 35 U.S.C.§120, claims benefit under 35 U.S.C. §119 of Japanese Patent ApplicationNo. 2006-118324, filed on Apr. 21, 2006, and incorporates the entirecontents of both of those prior applications by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiation detection system for use indiagnoses in a hospital, and a radiation imaging apparatus appropriateas an industrial non-destructive inspection apparatus. In thisspecification, electromagnetic waves such as X-rays, γ-rays, etc., aswell as particulate beams such as α-rays and β-rays, are included in“radiation”.

2. Description of the Related Art

With the progress of recent thin film semiconductor processingtechnology for radiography, apparatuses have been developed forradiographing an X-ray image using a semiconductor sensor. These X-raydetectors can be produced in a relatively flat structure, and arereferred to as a flat panel X-ray detector (“flat panel detector”, or“FPD”). The FPD can be an indirect FPD or a direct FPD. The indirect FPDconverts X-rays into visible light through a phosphor, and detects thelight using an amorphous optoelectronic conversion element and a switchelement. The direct FPD does not use a phosphor, but uses amorphousselenium and the like, converts X-rays directly into electrons, anddetects them using an amorphous silicon switch element (TFT).

Presently, an image intensifier (I. I.) has become widespread as acommon detector for fluoroscopic radiography. The I. I. converts X-raysinto visible light by a scintillator, then converts theoptoelectronically intensified secondary electrons into visible lightagain, thereby obtaining an image by a CCD camera. Generally, since theI. I. has high sensitivity, it has been used for a patient to reduce thedosage of exposure to radiation when relatively long time fluoroscopicradiography is required in performing, for example, fluoroscopicradiographing for gastric surgery, surgery on the heart or brain, etc.,while inserting a catheter into a vein, and the like.

On the other hand, since a system using the FPDs can momentarily convertan X-ray image into digital data, it has become widespread as aradiographing apparatus capable of performing fluoroscopicradiographing. Although the I. I. has the advantage of high X-raysensitivity, it also has some problems of, for example, halation at highdosage of exposure to radiation because of a narrow dynamic range,distortion of surrounding images by an electronic lens, poor durability,a heavy device, etc.

To overcome the above-mentioned problems, a new fluoroscopicradiographing detector as a new replacement for the I. I. can be an FPDhaving a wide dynamic range, less image distortion, and lessdegradation. A mobile X-ray imaging apparatus using such an FPD isdisclosed in Japanese Patent Application Laid-Open No. 2005-000470.

Additionally, Japanese Patent Application Laid-Open No. 11-009579discloses an X-ray imaging apparatus that has a mechanism of connectingto and disconnecting from an X-ray detection unit for a C arm, and caneasily exchange various flat panel detectors having differentcapabilities and specifications in radiograph size, resolution, etc.

SUMMARY OF THE INVENTION

Generally, when fluoroscopic radiographing is performed, a pulsegenerating radiation source is used to reduce the dosage of exposure toradiation for a patient. The source can be of a rotating anode typecapable of suppressing heat generation by rotating an anode membercalled a target for triggering off collision between acceleratedelectrons for generation of X-rays, and of a fixed anode type withoutrotation. The X-ray generation apparatus (radiation source) of therotating anode type can generate X-rays of high dosage, and isappropriate for high-speed fluoroscopic radiographing. By contrast,since the X-ray generation apparatus of the fixed anode type cannotgenerate large amount of X-rays instantaneously, it is not appropriatefor high-speed radiographing.

In any case, there is the problem of heat generation from a radiationsource because it is necessary to irradiate an object with plural timesof emission of X-ray pulses for several seconds to several minutes, orfor a longer time, in fluoroscopic radiographing.

Additionally, the FPD generally reads an electrical signal obtained byconverting an X-ray into signal charge through an amorphous siliconswitch element (TFT). Therefore, it requires a driving circuit unit fordriving a TFT and a read-out circuit unit for detecting a signal throughthe TFT. In a medical device for reading low X-ray signal charge, strictspecifications and reliability far advanced from consumer products arerequired. The read-out circuit unit is provided with an operationalamplifier for each signal wiring, and one read-out circuit is configuredby a number of operational amplifiers. Generally, a radiographic arearequested for a flat panel X-ray detector depends on a radiographedportion, that is, as a square, it is a 20 to 25 cm square for a heartimage, a 30 to 35 cm square for a stomach portion, and a 35 to 45 cmsquare for a chest portion. If a 41 cm square X-ray detection element isconfigured with 160 μm pitches, 2560×2560 picture elements are required.When a read-out circuit unit is prepared for such a large number ofpicture elements generated in thin film semiconductor processing, anintegrated circuit (IC, LSI) in common semiconductor technology isgenerated. However, plural divided read-out circuit units are used dueto the size of a silicon wafer and the semiconductor process forgenerating it. For example, 40 chips are required for 64 channels, 20chips are required for 128 channels, and 10 chips are required for 256channels. The driving circuit unit is designed in the same manner.

To attain a high S/N ratio, each input unit (initial stage portion) ofthe read-out circuit unit is to be configured by an operationalamplifier. Especially when fluoroscopic radiographing is performed, itis necessary to provide an operational amplifier for the initial andsubsequent stage portions to reduce the dosage of exposure to radiationso that the X-ray detection signal can be amplified. For example, in thecase of a 256-channel IC, 10 chips are to be provided with 512 or moreoperational amplifiers for each chip. Then, the power consumption soars,and the problem of heat generation from the flat panel X-ray detectorarises.

When the heat generated from the IC is applied to the flat panel X-raydetector, the dark current of the X-ray detection element increases, andthe leak current of the TFT element also increases, thereby causing theincrease in noise. These conditions degrades the graininess of an image,causes an artifact which is not the information about an object, therebyexceedingly degrading the image quality. That is, it is the problem ofreducing the efficiency of an X-ray image diagnosis.

Furthermore, in the fluoroscopic radiographing, the X-ray detector hasto be driven for several seconds to several minutes, or longer dependingon each case. Therefore, as compared with still image drive, the heatgeneration from the X-ray detector, especially from the read-out circuitunit and the AD conversion circuit unit (ADC) cannot be ignored.Furthermore, in the fluoroscopic radiographing, it is necessary toincrease the number of ADCs as compared with still images, therebypossibly increasing the heat generation from the ADC.

Furthermore, in the fluoroscopic radiographing, when it is necessary totransmit the digital data converted by the ADC to the body severalmeters to tens meter apart, a line driver and a line receiver arerequired in transmitting the digital data at a high speed, which alsocauses the problem of heat generation from the electric parts.

Furthermore, in the state of the FPD connected to the C arm, heat isconducted and radiated by exchange through the connection point with theC arm while the heat radiation environment becomes poor in the state ofthe FPD separated from the C arm. Therefore, the heat generation of FPDis a problem in the state of the FPD separated from the C arm.

The present invention has been developed to solve the above-mentionedproblems and the objective of the present invention is to provide aradiation imaging apparatus capable of reducing undesired influence bythe heat generation of the FPD in the state of the FPD separated fromthe C arm, and capable of performing radiographing both in the state ofthe FPD connected to the C arm and in the state of the FPD separatedfrom the C arm.

The present invention aims at providing a radiation imaging apparatuscapable of easily obtaining high quality images and both connectingstate radiographing performed in the C arm connected state andnon-connecting state radiographing performed in the C arm disconnectedstate.

The radiation imaging apparatus according to the present inventionincludes a flat panel detector, a holding unit for holding at least theflat panel detector, and a control unit for controlling the flat paneldetector. With the configuration, the flat panel detector can beconnected to and disconnected from the holding unit, connecting stateradiographing can be performed with the flat panel detector connected tothe holding unit, and non-connecting state radiographing can beperformed with the flat panel detector disconnected from the holdingunit, the control unit controls the flat panel detector such that a heatgeneration quantity of the flat panel detector during the non-connectingstate radiographing can be lower than a heat generation quantity of theflat panel detector during the connecting state radiographing.

According to another aspect of the invention, the radiation imagingapparatus comprises a flat panel detector including picture elementsarranged in a matrix of rows and columns on a substrate, each pictureelement having a conversion element for converting radiation into anelectrical signal, a signal wiring connected to the picture elements ina column, and a read-out circuit unit connected to the signal wiring. Aholding unit holds the flat panel detector, and a control unit controlsthe flat panel detector. The flat panel detector can be connected to anddisconnected from the holding unit, and connecting state radiographingcan be performed with the flat panel detector connected to the holdingunit, and non-connecting state radiographing can be performed with theflat panel detector disconnected from the holding unit. In addition, thecontrol unit controls the flat panel detector so that a power supplyvoltage applied to the read-out circuit unit in the non-connecting stateradiographing is lower than that of applied to the read-out circuit unitin the connecting state radiographing, and so that a change incharacteristics of the read-out circuit unit due to a change of thepower supply voltage is compensated for.

A method of controlling a radiation imaging apparatus according to thepresent invention includes having a flat panel detector, a holding unitfor holding at least the flat panel detector, capably connecting theflat panel detector to and disconnected it from the holding unit,performing connecting state radiographing with the flat panel detectorconnected to the holding unit, and performing non-connecting stateradiographing with the flat panel detector disconnected from the holdingunit. With the configuration, the flat panel detector is controlled suchthat a heat generation quantity of the flat panel detector during thenon-connecting state radiographing can be lower than a heat generationquantity of the flat panel detector during the connecting stateradiographing.

The method of controlling the radiation imaging apparatus according tothe present invention controls the flat panel detector such that powerconsumption of the flat panel detector during the non-connecting stateradiographing can be lower than power consumption of the flat paneldetector during the connecting state radiographing.

A computer-readable storage medium storing a program used to direct acomputer to control the radiation imaging apparatus according to thepresent invention allows the computer to control the radiation imagingapparatus to have a flat panel detector, a holding unit for holding atleast the flat panel detector, capably connect the flat panel detectorto and disconnected it from the holding unit, perform connecting stateradiographing with the flat panel detector connected to the holdingunit, and perform non-connecting state radiographing with the flat paneldetector disconnected from the holding unit. With the configuration, theprogram allows the computer to control the flat panel detector such thata heat generation quantity of the flat panel detector during thenon-connecting state radiographing can be lower than a heat generationquantity of the flat panel detector during the connecting stateradiographing.

The computer-readable storage medium storing a program used to direct acomputer to control the radiation imaging apparatus according to thepresent invention allows the computer to control the flat panel detectorsuch that power consumption of the flat panel detector during thenon-connecting state radiographing can be lower than power consumptionof the flat panel detector during the connecting state radiographing.

According to the present invention, the heat generation quantity of theflat panel detector can be suppressed even if the heat radiationenvironment of the flat panel detector is poor during the non-connectingstate radiographing.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the configuration of the circuit of the X-raydetector in the X-ray imaging apparatus according to the first mode forembodying the present invention.

FIG. 2 illustrates the configuration of the circuit of the X-raydetector in the X-ray imaging apparatus according to the first mode forembodying the present invention.

FIG. 3 illustrates the two-dimensional expression of the pictureelements illustrated in FIGS. 1 and 2.

FIG. 4 illustrates an example of the circuit describing the inside ofthe drive circuit illustrated in FIG. 3.

FIG. 5 is a timing chart illustrating the operation of the drive circuitillustrated in FIG. 3.

FIG. 6 illustrates an example of the circuit describing the inside ofthe read-out circuit illustrated in FIG. 3.

FIG. 7 is a timing chart illustrating the operation of the read-outcircuit shown in FIG. 6.

FIG. 8 illustrates the circuit of the X-ray detector in the X-rayimaging apparatus according to the second mode for embodying the presentinvention.

FIG. 9 is a timing chart illustrating the operation illustrated in FIG.8.

FIG. 10 illustrates an X-ray imaging apparatus according to the secondmode for embodying the present invention, and illustrates a circuit forswitch of operational amplifier bias currents between connecting stateradiographing and non-connecting state radiographing.

FIG. 11 illustrates the two-dimensional expression of the pictureelements illustrated in FIGS. 1 and 2.

FIG. 12 illustrates the state (non-connecting state radiographing) ofthe operation of the X-ray detector according to the third mode forembodying the present invention.

FIG. 13 illustrates the read-out circuit unit of the flat panel X-raydetector according to the third mode for embodying the presentinvention, and the circuit unit for switch between “enable” and“disable”.

FIG. 14 illustrates the circuit of the flat panel X-ray detectoraccording to the fourth mode for embodying the present invention.

FIG. 15 is a timing chart illustrating the operation (connecting stateradiographing) according to the fourth mode for embodying the presentinvention.

FIG. 16 is a timing chart illustrating the operation (non-connectingstate radiographing) according to the fourth mode for embodying thepresent invention.

FIG. 17 is a timing chart illustrating the operation (non-connectingstate radiographing) according to the fifth mode for embodying thepresent invention.

FIG. 18 illustrates the X-ray imaging apparatus according to the sixthmode for embodying the present invention, and illustrates the structureof the C arm and the X-ray detector.

FIG. 19 illustrates the outline of the mobile X-ray imaging apparatus towhich the present invention can be applied.

FIG. 20 illustrates the outline of the mobile X-ray imaging apparatus towhich the present invention can be applied.

FIGS. 21A and 21B illustrate examples of the connection detection unit.

FIG. 22 illustrates the outline of detecting the connection state by theconnection detection unit provided at the C arm and controlling theX-ray imaging unit according to the control signal.

DESCRIPTION OF THE EMBODIMENTS

The mode for embodying the present invention is practically describedbelow by referring to the attached drawings.

(First Mode for Embodying the Present Invention)

FIG. 1 illustrates the configuration of the circuit of the flat panelX-ray detector (radiation imaging apparatus) according to the first modefor embodying the present invention. A picture element 101 is configuredmainly by an optoelectronic conversion element (PD), and a switchelement (TFT). The PD can be an X-ray detection element for convertingan X-ray directly into electric charge or a photodiode for convertingvisible light into charge. When it is a photodiode, a phosphor (notillustrated in the attached drawings) for temporarily converting anX-ray into visible light is required. The optoelectronic conversionelement PD is biased by the voltage Vs from a power supply control unit104, and the gate voltage of the TFT is driven by the signal from adrive circuit unit 103. The drive circuit unit 103 is a shift register.The gate-on voltage (gate voltage) of the TFT is determined by thevoltage Vcom applied from the power supply control unit 104 to the drivecircuit unit 103. The gate-off voltage of the TFT is determined by thevoltage Vss applied also from the power supply control unit 104 to thedrive circuit unit 103. The signal of the optoelectronic conversionelement PD is output to a read-out circuit unit 102 through the TFT.

The initial stage portion of the read-out circuit unit 102 is configuredby an operational amplifier (AMP1), and is an integration circuit.Capacitors CF1 and CF2 in the integration circuit of the operationalamplifier AMP1 can be switched by a signal GAIN1 from a timinggeneration unit 107. The output of the operational amplifier AMP1 isinput to the operational amplifier (AMP2) at the next stage through thecapacitor C3. Capacitors C4 and C5 connected to the feedback terminal ofthe operational amplifier AMP2 can be switched by a signal GAIN2, andthe amplification rate (gain) of the operational amplifier AMP2 can beselected. The output of the operational amplifier AMP2 is accumulated bya capacitor C6 for sampling and holding, and is then output to an ADconversion unit 105 through an operational amplifier (AMP3) at thesubsequent stage. The AD converted digital data is stored in the memoryof an arithmetic operation unit 106. The operational amplifiers AMP1,AMP2 and AMP3 are operated by a “+” side power supply voltage Vdd and a“−” power supply voltage Vee. The power supply voltage of the ADconversion unit 105 is Vcc. The timing generation unit 107 provides adigital signal required by the drive circuit unit 103 and the read-outcircuit unit 102. The arithmetic operation unit 106 includes a CPU, andcontains memory.

In the present mode for embodying the present invention, at aninstruction from the arithmetic operation unit 106 containing the CPU,each power supply in the power supply control unit 104 can provideplural power supply voltages. The X-ray imaging apparatus illustrated inFIG. 1 has the configuration of connecting it to the end portion of aC-shaped support arm (C arm) 16 as illustrated in FIG. 19, and is alsoconfigured to perform radiographing with the arm disconnected from theapparatus as illustrated in FIG. 20.

FIGS. 19 and 20 illustrate the mobile X-ray imaging apparatus applicableto the X-ray imaging apparatus according to the present invention. Aflat panel X-ray detector 11 includes an X-ray detection sensor having adetection plane on which a plurality of optoelectronic conversionelements is arranged in a two-dimensional array, and an electricalcomponent unit. The flat panel X-ray detector 11 is connected to aconnection mechanism 19. A radiation source 12 is fixed through a pairof support panels 17.

As illustrated in the figures, the radiation source 12 and the flatpanel X-ray detector are fixed to the C-shaped support arm (C arm) 16.The C arm 16 is connected to a column 14 through connection mechanisms15 and 26. With this configuration, the radiation source 12 is fixedwith the center of the emitted X-rays matching the center of thedetection plane of the image detection unit 11.

The C arm 16 can be turned clockwise or counterclockwise using theconnection mechanisms 14 and 15, and moved upwards and downwards alongthe column 14, thereby improving convenience during radiographing. Amobile X-ray generation apparatus 13 has wheels 25, and can be movedeasily in a hospital. A control unit 20 controls the X-ray generationapparatus, a control unit 21 controls the flat panel X-ray detector, andreference numeral 22 designates an operation and display unit.

FIG. 20 illustrates the state in which the flat panel X-ray detector 11is removed from the connection mechanism 19 as a change from the stateillustrated in FIG. 19. The flat panel X-ray detector 11 is mountedbetween a bed 24 and an object 23 laying on the bed 24 on his or herback. When the flat panel X-ray detector 11 is removed from theconnection mechanism 19, wireless communication can be performed to andfrom the control unit 21, and a control signal and image data arecommunicated by wireless. The radiation source 12 is aligned above theflat panel X-ray detector 11 at the position where the X-rays can beemitted perpendicularly to the detection plane of the flat panel X-raydetector 11.

For the alignment, the C arm 16 rotates counterclockwise roughly 45°within the plane of the paper from the position illustrated in FIG. 20.The radiation source 12 rotates clockwise roughly 45° (in the Adirection) from the position illustrated in FIG. 19 on the support panel17 using a support axis 18 as the rotation center. The rotation can bemade counterclockwise (in the B direction) depending on the conditions.The radiation source 12 can also be rotated in the C and D directions onthe tangent of the arc of the C arm 16 as well as the support panel 17.The column 14 can also be rotated on the vertical axis, and the entire Carm 16 can be rotated on the vertical axis. Since the radiation source12 can be moved with the degree of freedom, the image detection unit canbe disconnected from the fixed mechanism so that X-rays can beirradiated at an appropriate position anywhere the unit is mounted.

In FIG. 19, the C arm (holding unit) 16 holds the flat panel X-raydetector 11 and the radiation source 12. The flat panel X-ray detector11 can be connected to and disconnected from the C arm 16. Both theconnecting state radiographing with the flat panel X-ray detector 11connected to the C arm 16 and the non-connecting state radiographingwith the flat panel X-ray detector 11 disconnected from the C arm 16 canbe performed. The arithmetic operation unit 106 and the power supplycontrol unit 104 control the flat panel X-ray detector 11 such that theheat generation quantity of the flat panel X-ray detector 11 during thenon-connecting state radiographing can be lower than the heat generationquantity of the flat panel X-ray detector 11 during the connecting stateradiographing. Practically, the arithmetic operation unit 106 and thepower supply control unit 104 control the flat panel X-ray detector 11such that the power consumption of the flat panel X-ray detector 11during the non-connecting state radiographing can be lower than thepower consumption of the flat panel X-ray detector 11 during theconnecting state radiographing. Preferably, they perform control suchthat the power consumption of the read-out circuit unit 102 during thenon-connecting state radiographing can be lower than the powerconsumption of the read-out circuit unit 102 during the connecting stateradiographing.

The radiographing performed when the flat panel X-ray detector isconnected to the C arm 16 as illustrated in FIG. 19 is referred to as“connecting state radiographing”, and the radiographing performed whenthe flat panel X-ray detector is disconnected from the C arm 16 asillustrated in FIG. 20 is referred to as “non-connecting stateradiographing”. In the connecting state radiographing and thenon-connecting state radiographing, at least one of the sensor bias Vsin the power supply control unit 104, the TFT on voltage Vcom, the powersupply voltages Vdd and Vss of the operational amplifier in the read-outcircuit unit 102, and the power supply voltage of the AD conversion unit105 is switched. That is, in the non-connecting state radiographing, ascompared with the connecting state radiographing, control is performedsuch that the power supplied to the flat panel X-ray detector can belower (the power supply voltage van be lower), and the heat generationquantity during the non-connecting state radiographing is suppressed ascompared with the connecting state radiographing.

The arithmetic operation unit 106 and the power supply control unit 104control the flat panel X-ray detector 11 such that the power supplyvoltages Vdd and Vee of the read-out circuit unit 102 during thenon-connecting state radiographing can be lower than the power supplyvoltages Vdd and Vss of the read-out circuit unit 102 during theconnecting state radiographing. Furthermore, they control the flat panelX-ray detector 11 such that the bias Vs of the conversion element PD orthe drive voltage Vcom of the switch element TFT during thenon-connecting state radiographing can be lower than bias Vs of theconversion element PD or the drive voltage Vcom of the switch elementTFT during the connecting state radiographing.

The X-ray imaging apparatus conducts heat and radiate the heat byexchange through connection points to the C arm with the flat panelX-ray detector 11 connected to the C arm. The details are describedbelow by referring to FIG. 18. When the flat panel X-ray detector 11 isnot connected to the C arm, the heat radiation environment is poor.Therefore, in the present mode for embodying the present invention, whenthe flat panel X-ray detector 11 is not connected to the C arm, thevoltage of the flat panel X-ray detector 11 is reduced, the power supplyis reduced, and the heat generation quantity is suppressed as comparedwith the state in which the flat panel X-ray detector 11 is connected.

Generally, the voltages Vdd and Vss depend on the production process ofan operational amplifier. If a power supply voltage is changed, variouscharacteristics of the amplifier also change in many cases. For example,the operational amplifier AMP1 accumulates a signal from the pictureelement 101 in the capacitor CF1, but the amount of charge accumulatedin the capacitor CF1 changes if the power supply voltage of theoperational amplifier AMP1 drops. That is, what is called a dynamicrange changes. In this case, during the connecting state radiographingand the non-connecting state radiographing, not only the power supplyvoltage, but also the capacitor CF2 can be added for use. That is, whenthe characteristic by a change of a power supply voltage changes, it isto be grasped in advance, and the drive to compensate for it is to beperformed.

There can be a case in which a power supply voltage cannot be largelychanged with respect to the reliability of an operational amplifier. Inthis case, the precision of the power supply of the power supply controlunit 104 is to be improved, and can be switched in the range of therecommended operation condition (for example, 5 V±0.5).

The power supply Vcc of the AD conversion unit 105 is similar to Vdd andVss. The Vs of the picture element 101 does not require an enormouslylarge amount of current as compared with the operational amplifier.However, since there are a large number of picture elements, and theX-ray detection element and the switch element have temperaturecharacteristics, it is desired that the power supply control unit 104changes the power consumption between the connecting state radiographingand the non-connecting state radiographing.

Especially, when a direct X-ray detection element is used, 0.5 to 1 mmthick amorphous selenium is generally evaporated. Therefore, a higherelectric field is required than the indirect type, and the voltage of5000 to 10000 volts is to be applied to the bias Vs applied to the X-raydetection element. In the present mode for embodying the presentinvention, the Vs power supply voltage in the non-connecting stateradiographing can be switched to avoid the problem of heat generation bythe high voltage.

Furthermore, by reducing the power supply voltage of the read-outcircuit unit 102, the dynamic range of the read-out circuit unit 102 isreduced. To compensate for the reduction, Vs and Vcom can be reduced.

FIG. 2 illustrates the configuration of the circuit of the flat panelX-ray detector in the X-ray imaging apparatus according to the firstmode for embodying the present invention, and illustrates a circuitother than the circuit illustrated in FIG. 1. In FIG. 2, a circuitmember also illustrated in FIG. 1 is assigned the same referencenumeral.

The different point of FIG. 2 as compared with FIG. 1 is that theoperational amplifier (AMP1, AMP2, and AMP3) in the read-out circuitunit 102 is operated by a single power supply (Vdd), and the referencepotential (Vref1) connected to the non-inversion input terminal of eachoperational amplifier is supplied from the power supply control unit104. As described above by referring to FIG. 1, during thenon-connecting state radiographing, the power supply voltage Vdd isreduced and driven with the supply of power reduced, and the heatgeneration is suppressed. Then, if the corresponding reduction of thedynamic range and other inconvenient factors occur, the referencepotential Vref1 of the power supply control unit 104 can be changed.Furthermore, in FIG. 2, the Vref1 common line supplies the referencepotential of the operational amplifiers AMP1, AMP2, and AMP3. However,as necessary, another system can supply the potential. In this case, thepower supply control unit 104 provides three types of referencepotential (Vref1, Vref2, and Vref3) are provided, and each of them canbe independently switched.

FIG. 3 illustrates the picture element 101 illustrated in FIG. 1 as thetwo-dimensional expression of 6×6=36 picture elements. For example, tomedically radiograph the chest portion of a person, for example, theresolution of about 160 μm pitches is required for a photoreceiving areaof, for example, 41 cm×41 cm. In the case of 160 μm pitches for aphotoreceiving area of 41 cm×41 cm, the number of picture elements is2560×2560, that is, about 6.55 million picture elements.

In FIG. 3, S1-1 to S6-6 designate an optoelectronic conversion elementor an X-ray detection element (radiation detection element). In theindirect system, the material is amorphous silicon. In the directsystem, the material is amorphous selenium. The radiation detectionelement is biased by a sensor bias source Vs 1101. T1-1 to T6-6designate switch elements, and are generally made of amorphous siliconthin film transistor TFT regardless of the direct or indirect system. G1to G6 designate driving gate wiring for driving the TFT, and M1 to M6designate read wiring for reading a signal of a radiation detectionelement through the TFT. G1 to G6 are driven by a drive circuit unit1103 configured mainly by a shift register circuit. The read wiring M1to M6 are read by the read circuit unit 1102. The X-ray detectionelements S1-1 to S6-6, the switch elements T1-1 to T6-6, the gate wiringG1 to G6, and the signal wiring M1 to M6 are collectively referred to asa radiation detection circuit unit (radiation detection substrate) 1104.

The picture elements include conversion elements S1-1 to S6-6 that arearranged in a matrix array of rows and columns on the radiationdetection substrate 1104 and convert radiation into an electricalsignal, and switch elements T1-1 to T6-6. The drive wiring G1 to G6 areconnected to the switch elements T1 to T6-6 in the row direction. Thesignal wiring M1 to M6 are connected to the switch elements S1-1 to S6-6in the column direction, and transmit the electrical signal. The drivecircuit unit 1103 is connected to the drive wiring G1 to G6. The readcircuit unit 1102 is connected to the signal wiring M1 to M6.

FIG. 4 illustrates an example of a circuit of the inside of the drivecircuit unit 1103. It corresponds to the drive circuit unit 103 shown inFIG. 3. A shift register is configured by arranging a D flip-flop 1201and an AND element 1202 as illustrated in FIG. 4. They are controlled bythree signals, that is, an OE, a SIN, and a CPV. Generally, a Dflip-flip and an AND element are digital circuit, and the input/outputvoltage relates to a processing step for generating an element.Generally, the input/output voltage of a Hi logic is 5V system. However,with a recent request for lower power consumption and the progress ofprocessing technology, some devices have been released as systemsoperated with voltages of 3.3V or less. However, generally, the switchelement of the radiation detection substrate 1104 is made of amorphoussilicon, and it is desired that the drive voltage is 5V or more in thecurrent processing technology of producing amorphous silicon TFT.Therefore, a level shift circuit 1203 is provided for conversion into adrive voltage that matches the characteristic of the amorphous siliconswitch element TFT.

FIG. 5 is a timing chart illustrating an example of the operation of thedrive circuit unit (shift register) 1103 illustrated in FIG. 3. In thisexample, the output of G1 to G6 is shifted stage by stage.

FIG. 6 illustrates an example of a circuit of the inside of the readcircuit unit 1102 illustrated in FIG. 3. It corresponds to the read-outcircuit unit 102 illustrated in FIG. 1. However, for simplerexplanation, the portion of the operational amplifier AMP2 in theread-out circuit unit 102 illustrated in FIG. 1 is omitted. The portionof switching between the capacitors CF1 and CF2 in the operationalamplifier AMP1 is also omitted.

A1 to A6 designate operational amplifiers, and function as integratorsby configuring the capacitors CF1 to CF6 as illustrated in FIG. 6. SW1to SW6 are switch elements for resetting the integration charge of thecapacitors CF1 to CF6, and reset by the control signal RC. C1 to C6 areconversion elements for sampling and holding the signals of A1 to A6,and the signals are sampled and held by turning on and off the switchelements Sn1 to Sn6. The switch elements Sn1 to Sn6 are turned on andoff by the control signal SH. B1 to B6 designate buffer amplifiers forcorrectly transmitting the signal potential of the capacitors C1 to C6.Relating to their output, a signal from a shift register 1301 is appliedfrom the switch Sr1 to Sr6, a parallel signal is converted into a serialsignal, and output through an amplifier 1302.

FIG. 7 is a timing chart illustrating an example of the operation of theread circuit unit 1102 illustrated in FIG. 6. The operation of the drivecircuit unit (shift register) 1103 illustrated in FIG. 4 is alsodescribed.

First, the operation of the first row is described. The signal chargeoptoelectronically converted by the X-ray detection elements S1-1 toS6-1 is input to the operational amplifiers A1 to A6 of the read circuitunit 1102 through the signal wiring M1 to M6 after the switch elementsT1-1 to T6-1 are turned on by the G1 signal (transfer operation). As aresult, the signal charge is accumulated in the capacitors CF1 to CF6.Then, the signal SH reaches a high level (ON) and collectivelytransferred to the capacitor elements C1 to C6 for sampling and holding.Relating to the signals of the capacitors C1 to C6, the parallel data isrearranged into serial data in time series upon receipt of the signalsSr1 to Sr6 from the shift register 1301, and signals of one row areoutput (serial converting operation).

The operation for the second row is described below. According to theconfiguration illustrated in FIG. 6, after sampling and holding in thecapacitor elements C1 to C6 according to the sampling and holding signalSH in the data of the first row, the transfer operation of the data ofthe second row can be performed. That is, the capacitors CF1 to CF6 arereset by the signal RC, then the transfer operation by the G2 signal isperformed, and the serial conversion operation is performed. Similaroperations are repeated.

In the circuit illustrated in FIG. 6, the sampling and holding circuitenables the transfer operation in the (n+1)th row and the serialconversion operation in the n-th row to be performed concurrently.

The reading time Tr for one line is roughly a total of the time (RC) forresetting the integration capacitor, and the time in which the shiftregister of the drive circuit unit 1103 is turned on, that is, the TFTon time (OE) and the sampling and holding time (SH).Tr≈RC+OE+SH

The time Tr for one line is roughly a total of the pulse widths Sr1 toSr6 of the shift register 1301 of the read circuit unit 1102 and thesampling and holding time SH (Sr1+Sr2+ . . . Sr6+SH).Tr≈Sr1+Sr2+Sr3+Sr4+Sr5+Sr6+SH

The reading time Tf for 1 frame is calculated as follows when there aren lines (6 lines in FIG. 3).Tf=Tr×(n+1)(Second Mode for Embodying the Present Invention)

FIG. 8 illustrates an X-ray detection circuit in the X-ray imagingapparatus (radiation imaging apparatus) according to the second mode forembodying the present invention. FIG. 8 illustrates the inside of theoperational amplifier of the initial stage portion of the read-outcircuit unit 102, and illustrates the configuration of switching theamount of current of a current source 801 connected to the differentialtransistor pair (Q1, Q2) of the input unit.

Although FIG. 8 illustrates the circuit of one channel, one read-outcircuit unit (IC chip) 102 is configured by multiple channels of, forexample, 128 channels or 256 channels. Therefore, the amount of currentof the current source 801 required to operate the read-out circuit unit102, that is, to operate the operational amplifier, largely affects thepower consumption of the read-out circuit unit 102, thereby largelyinfluencing the heat generation from the IC chip.

In the present mode for embodying the present invention, the amount ofcurrent of the current source 801 can be switched between the connectingstate radiographing in which the C arm is connected as illustrated inFIG. 19 and the non-connecting state radiographing in which the C arm isremoved as illustrated in FIG. 20.

The arithmetic operation unit 106 controls the flat panel X-ray detector11 such that the amount of current of the current source 801 of theoperational amplifier during the non-connecting state radiographing canbe lower than the amount of current of the current source 801 of theoperational amplifier during the connecting state radiographing.

FIG. 9 is a timing chart illustrating the operation of the circuitillustrated in FIG. 8. FIG. 9 illustrates one line (Tr) shown in FIG. 7,and also illustrates the analog output (VAMP1) of the operationalamplifier AMP1.

The signal charge accumulated in the optoelectronic conversion element(X-ray detection element) PD in the radiation detection substrate 1104is defined as Q. The integration capacitor connected to the inversioninput terminal (−) of the operational amplifier AMP1 and the outputterminal VAMP1 is defined as CF1. The reference potential connected tothe non-inversion input terminal (+) is defined as Vref1, the outputpotential VAMP1 is expressed as follows.VAMP1=Vref1−(Q/CF1)

However, Vref1 is reference potential, and the output voltage by thesignal charge accumulated by the optoelectronic conversion element PD isdefined as Q/CF1. The object of the signal RC is to reset the capacitorCF1 by setting the operational amplifier AMP1 in the buffer state, andto reset the parasitic capacitor of the signal wiring from the TFT ofthe radiation detection substrate 1104 connected to the inversion inputterminal (−) although not illustrated in the attached drawings. Afterresetting the capacitor CF1 by the signal RC, the gate of the TFT isturned on for a high level time of the signal OE, and the signal chargeaccumulated by the optoelectronic conversion element PD of the next lineis accumulated by the capacitor CF. Simultaneously, the optoelectronicconversion element PD is reset to the reference potential Vref1, therebypreparing for the accumulating operation of the next frame.

Next, the operation performed when the operational amplifier is resetillustrated in FIG. 8 is described below. Generally, when the gatepotential of the transistors Q1 and Q2 of the first conductive typeconfiguring the differential transistor pair changes, the drain currentsIQ1 and IQ2 change as follows.IQ1=I+ΔIIQ2=I−ΔI

The drains of the transistors Q1 and Q2 are connected respectively tothose of the transistors Q3 and Q4 of the second conductive typeconfiguring the constant current source, and the differential current isinput to the gate grounding transistors Q5 and Q6 of the secondconductive type. When the current passes through the transistor Q5, itis input to the current mirror circuit configured by the transistors Q7to Q10 of the first conductive type. By charging and discharging thephase compensation capacitor Cp due to the differential current 2ΔIbetween the output current, that is, the drain current Q8 of thetransistor Q8, and the current IQ6 that has passed the transistor Q6,the output voltage VAMP1 can be changed.IQ8=I1−(I+ΔI)IQ6=I1−(I−ΔI)IQ6−IQ8=2ΔI

The change of the output voltage AMP1 is fed back to the gate electrodeof the transistor Q2 that is an inversion input terminal (−) of anoperational amplifier, and is stabilized at ΔI=0.

When the resent switch RC is turned on, the output terminal VAMP1momentarily placed in the signal output state. Therefore, the gatepotential of the transistor Q2 is lower than the gate potential of thetransistor Q1 by the signal voltage Q/CF1. Therefore, the transistor Q1is turned on, and the transistor Q2 is turned off. The change of thedrain currents of the resultant transistors Q1 and Q2 is expressed asfollows.ΔI=I

Therefore, the phase compensation capacitor Cp is charged by the biascurrent 2I of the differential transistor pair Q1 and Q2, and the timerequired to 1V change the output voltage VAMP1, that is, the reciprocalof the through rate SR of the operational amplifier AMP1, is expressedby the following equation.1/SR(sec/V)=Cp/2I

Therefore, the reset time RC requires at least the time obtained bymultiplication by the signal voltage Vsig=Q/CF1.RC=Vsig/SR=Q/CF1×(Cp/2I)

That is, to shorten the reset time RC, the value of the phasecompensation capacitor Cp is reduced, or the bias current value 2I inthe current source 801 is increased.

However, at the time of reset by the signal RC, the operationalamplifier is a buffer amplifier. Therefore, if the value of the phasecompensation capacitor is reduced, the system becomes unstable. As aresult, for a stable system at the time of reset, the value of thecapacitor Cp is relatively large. To charge it and raise the throughrate SR, a large bias current value is required. A large bias currentvalue is required. The bias current is a DC current to be consumed inthe reading period in addition to the reset period, thereby increasingthe power consumption of the entire system.

That is, to shorten the time required to read one line for a high-speedoperation, the bias current is to be raised to improve the through rate.On the other hand, in this method, the power consumption increases andthe heat generation also increases. Thus, the speed is traded offagainst the power consumption (heat generation).

In the non-connecting state radiographing in which the C arm isdisconnected as illustrated in FIG. 20, the heat radiation environmentof the flat panel X-ray detector is different from the environment ofthe connecting state radiographing in which the flat panel X-raydetector is connected to the C arm. Therefore, in the present mode forembodying the present invention, the amount of the bias current of thecurrent source of the operational amplifier is switched to suppress theheat generation quantity.

FIG. 10 illustrates a circuit for switching the amount of bias currentby the current source of the operational amplifier between theconnecting state radiographing and the non-connecting stateradiographing according to the present mode for embodying the presentinvention. In FIG. 10, the connection between the differentialtransistor pair configuring the first stage and the current sourcesconnected to them is illustrated as an example of connecting circuitsconfigured by multiple channels.

Reference numeral 1009 designates an operational amplifier, referencenumeral 1010 designates a constant voltage source, and reference numeral1011 designates a switch for switching between connecting stateradiographing and non-connecting state radiographing.

The current Ir1 flowing through the transistors Q1 and Q3 is determinedby the resistor values R1 and R2 connected to the Vr, the node A, andthe GND, and calculated as the Ir1=Vr/(R1+R2) when the switch 1011 isturned off.

Since the transistors Q2 and Q4 are configured as current mirrors, thecurrent is Ir1, and similarly the Ir1 flows through the current sourceconnected to the differential transistor pair of the operationalamplifier.

In the read-out circuit unit in which 256 channels are connected to theinput stage, a constant bias current of 256 times Ir1 flows.Furthermore, when not only the initial stage unit but also the nextstage are configured by operational amplifiers, further double biascurrent flows. When the switch 1011 is turned on, and when theon-resistor of the switch is ideally zero, the resistor value connectedto the node A and the GND is R1, and the current Ir2 flowing through thetransistor Q1, Q2, Q3, and Q4 is Ir2=Vr/R1, and Ir2>Ir1.

In the present mode for embodying the present invention, the switch 1011is turned on during the connecting state radiographing, and a switch1012 is turned off during the non-connecting state radiographing,thereby switching the current consumption.

In the description relating to FIG. 10, the bias current is switched byswitching the resistor value, but the voltage value VR of the constantvoltage source 1010 connected to the operational amplifier 1009 can alsobe switched.

In the connecting state radiographing and the non-connecting stateradiographing, the current consumption can be lower, that is, the heatgeneration quantity can be smaller, in the non-connecting stateradiographing. On the other hand, since the time required at the resettime increases, the speed is lower in the non-connecting stateradiographing. Since the heat generation quantity depends on thesequence of drive in each radiographing system, the resistor values R1and R2 and the voltage value VR can be set depending on the situation.

For example, in the connecting state radiographing with the C armconnected as illustrated in FIG. 19, high-speed fluoroscopicradiographing is performed while in the non-connecting stateradiographing as illustrated in FIG. 20, the still image radiographingcan be performed.

Furthermore, in the non-connecting state radiographing illustrated inFIG. 20, radiographing is performed using an X-ray source fixed to thebody of the C arm. However, the source is not limited to this, butanother X-ray source can be used.

Also in the connecting state radiographing, high-speed fluoroscopicradiographing is performed. In the non-connecting state radiographing,the still image radiographing or the low-speed and simple fluoroscopicradiographing can also be performed.

During the non-connecting state radiographing, when the high-speedfluoroscopic radiographing equivalent to the connecting stateradiographing is requested, the radiographing time can be restrictedwith the state of heat generation taken into account.

(Third Mode for Embodying the Present Invention)

FIG. 11 illustrates the radiation detection circuit unit 1104 in thetwo-dimensional array using 6×6=36 picture elements as illustrated inFIG. 3. The difference from FIG. 3 is that the signal wiring (verticalwiring in FIG. 11) M1 to M6 connected to the TFT are separated at thecenter, and the read-out circuit unit (1102, 1112) are directed upwardand downward. In addition, the drive circuit unit 103 for drive of thegate wiring (horizontal wiring in FIG. 11) G1 to G6 of the TFT isprovided left and right. The gate wiring G1 to G6 are not separated atthe center.

Thus, by separating the signal wiring M1 to M6 at the center, forexample, the row G1 and the tow G4 can be simultaneously driven. Next,since the row G2 and the row G5 can be simultaneously driven and the rowG3 and the row G6 can be simultaneously driven, the reading time for oneframe can be about half the time illustrated in FIG. 3. That is a higheroperation can be realized. By connecting the drive circuit unit 1103 atright and left, the delay of the gate drive pulse and the deformation ofa waveform caused by the wiring resistance of the gate wiring G1 to G6and the wiring capacitor can be prevented or reduced. Since thedeformation of a waveform of the gate wiring G1 to G6 causes variancesin offset output waveform, it is desired that the drive circuit units1103 are simultaneously driven from both right and left as illustratedin FIG. 11.

On the other hand, as compared with FIG. 3, in the circuit configurationin FIG. 11, there have to be a double number of read-out circuit unitsand driving circuit units respectively.

For example, to medically radiograph a chest portion of a person, for a41 cm×41 cm light receiving area, the resolution of 160 μm pitches isrequested. For a 41 cm×41 cm light receiving area with 160 μm pitches,the number of picture elements are 2560×2560=about 6.55 million pictureelements.

As an example, when each IC of the read circuit units 1102 and 1112 isconfigured by 320 channels, the required number of read circuit units(IC) 1102 and 1112 is, in the case shown in FIG. 11, a total of 16including the upper and lower units. When the IC of the drive circuitunit 1103 is configured by 320 channels per unit, the required number ofdrive circuit units (IC) 1103 is 16 including the left and right units.FIG. 12 illustrates the outline of the installed state of the example.

FIG. 12 illustrates an example of the operation of the flat panel X-raydetector in the non-connecting state radiographing according to thethird mode for embodying the present invention. The present mode forembodying the present invention drives the entire IC in the connectingstate radiographing when the C arm is connected. In the non-connectingstate radiographing in which the C arm is disconnected, only thecorresponding read circuit units 1102, 1112, and drive circuit unit 1103are operated (enabled) depending on the X-ray irradiation area(irradiation field). The read circuit units 1102 and 1112 and the drivecircuit unit 1103 other than the X-ray irradiation area are not operated(disabled). When the boundary of the X-ray irradiation area is in thechannels of the read circuit units 1102 and 1112, the read circuit is“enabled”. When the boundary of the X-ray irradiation area is in thechannels of the drive circuit unit 1103, the drive circuit is “enabled”

The switch between “enable” and “disable” is performed according to acontrol signal input to each IC. When the IC is set as “disabled”, thepower consumption is much lower and the heat generation quantity issmaller than the IC set as “enabled”.

The X-ray irradiation area is selected by a collimator provided near theemission unit of X-ray source to automatically control the collimator,or to manually determine it.

The read circuit units 1102 and 1112, and the drive circuit unit 1103can be selected by, for example, once scanning the radiation detectioncircuit unit 1104 in advance, recognizing the irradiation field from thedata of the read circuit units 1102 and 1112, and reflecting the resultby the subsequent radiographing (in the case of moving imageradiographing).

Otherwise, a radiographing engineer can manually determine theirradiation field in advance, and depending on the determination, theread circuit units 1102 and 1112 and the drive circuit unit 1103 can beselected.

FIG. 13 illustrates an example of the circuit of switching “enable” and“disable” in the read circuit units 1102 and 1112 of the flat panelX-ray detector according to the third mode for embodying the presentinvention. FIG. 13 is different from FIG. 10 in that it includes aswitch 1012 between the gates of the transistors Q1 and Q2 and the powersupply. When the switch 1012 is turned on, the PMOS (Q2) is turned off,no current flows to the current source connected to the differentialtransistor pair of each channel, and no operation of the operationalamplifier is performed. That is, the power consumption becomes extremelylow, and the heat generation is suppressed.

In FIG. 12, the control signal is provided for each IC. However, sincethe boundary of the X-ray irradiation field can be in the channel, aplurality of control lines can be provided in each IC for more efficientcontrol.

FIG. 13 illustrates the control of the current source of the operationalamplifier at the initial stage. However, when operational amplifiers arecascaded at the second and third stages, similar connection can be madefor control. In this case, the current sources of 320 channels×3=960operational amplifiers are stopped per chip, thereby largely suppressingthe power consumption, and then considerably reducing the heatgeneration quantity.

In the non-connecting state radiographing, the arithmetic operation unit106 controls the flat panel X-ray detector 11 to operate the readcircuit units 1102 and 1112 and the drive circuit unit 1103 for theX-ray (radiation) irradiation field, but to set the read circuit units1102 and 1112 and the drive circuit unit 1103 for a field outside theX-ray (radiation) irradiation field at a non-operating state or at astate of reduced current consumption.

(Fourth Mode for Embodying the Present Invention)

FIG. 14 illustrates the circuit of the picture elements according to thefourth mode for embodying the present invention. In FIG. 14, the controlterminal for cutting off (disable) a bias current of an operationalamplifier described by referring to the third mode for embodying thepresent invention is assigned a terminal name “IDLE”. Furthermore, thecontrol terminal for switching the amount of bias current of anoperational amplifier described by referring to the second mode forembodying the present invention is assigned a terminal name “BIAS”.Signal wiring is connected from the picture elements to the inversioninput terminal of the operational amplifier (AMP1). The non-inversioninput terminal of the operational amplifier (AMP1) is assigned thepotential of Vref1 by a reference potential 1015. The switch 1013 isconnected to the output terminal of the operational amplifier (AMP1)through a protective resistor so that the signal IDLE controls theoutput terminal to be connected to the Vref1. That is, when the signalIDLE is turned on, an OR circuit 1016 turns on the switch 1017, thecontrol of the signal RC cannot work, and the signal wiring from theinversion input terminal (−) of an operational amplifier, that is, theflat panel X-ray detector (X-ray detection substrate), is biased to theVref1.

In other words, the output terminal and the inversion input terminal canbe equivalent in potential without operating the operational amplifierAMP1 in the buffer state, which is advantageous in power consumption.

When an X-ray detection element (optoelectronic conversion element) isconfigured by a material such as amorphous silicon and the like, theelement immediately after power-up is not stable in dark current, and itis necessary to perform a pseudo-drive for a while. The pseudo-drive isreferred to as idling. Operating an operational amplifier (enable) inthe idling period consumes electric power and heat generation occurs.

Therefore, in the period, the flat panel X-ray detector performs theidling operation, and it is desired that the operational amplifier is inthe “disabled” state. Thus, the total power consumption for theradiographing operation can be reduced. In the present mode forembodying the present invention, the operational amplifier is placed inthe “disabled” state according to the signal IDLE, and the bias of theVref1 is applied to the signal wiring of the flat panel X-ray detectorthrough the switch 1017 from the output terminal of the operationalamplifier. Thus, the idling operation can be performed by supplying thegate voltage of the TFT and the bias of the photodiode.

FIG. 15 is a timing chart illustrating the operation according to thepresent mode for embodying the present invention, and illustrates thetiming in connecting state radiographing. The operation of the X-raydetector is represented by “FPD”.

Part (a) of FIG. 15 illustrates an example in which X-ray pulses arecontinuously emitted, and one frame of image data is read from the FPDwhile the X-rays are not emitted. The radiographing is an example offluoroscopic radiographing.

Part (b) of FIG. 15 also illustrates an example of fluoroscopicradiographing. It illustrates an example of reading one frame of imagedata and one frame of FPN (fixed pattern noise) data from an FPD whileX-rays are not being emitted in the period when pulses of X-rays arecontinuously emitted. By subtracting the FPD from the image data, thefixed pattern noise of the flat panel X-ray detector and the afterimagecomponents of optoelectronic conversion element are removed. Part (b) ofFIG. 15 indicates a half reduced frame rate as compared with part (a) ofFIG. 15.

Part (c) of FIG. 15 illustrates an example of inserting still imageradiographing while performing fluoroscopic radiographing illustrated bypart (a) of FIG. 15. Since still image radiographing data is commonlyused in a detail diagnosis, more X-rays are emitted than the X-raysemitted during fluoroscopic radiographing. In the drawing, FPN data iscollected in the still image radiographing while the FPN data is notcollected in the fluoroscopic radiographing. In part (c) of FIG. 15, thefluoroscopic radiographing is performed again after the still imageradiographing, but the process can be terminated by the still imageradiographing.

In parts (a), (b), and (c) of FIG. 15, the IDLE terminal is in the “lowlevel (Lo)” in any period, that is, the switch 1012 and the switch 1013are turned off, but the operational amplifier AMP1 is operating in the“enabled” state.

FIG. 16 is a timing chart illustrating the operation according to thepresent mode for embodying the present invention, and illustrates thetiming in the non-connecting state radiographing. FIG. 16 describes thesequence of the still image radiographing.

FIG. 16 illustrates the “disabled” state in which the bias current of anoperational amplifier is cut off by turning the IDLE terminal to the“high level (Hi)” (on) until the still image radiographing is performedto reduce the power consumption and suppress heat generation. However,in the period, although not illustrated in the attached drawings, a biasis applied to the drive of the TFT and the sensor, and the X-raydetection circuit is placed in the idling operation state.

When a request for the still image radiographing is issued, pulses ofX-rays are emitted, the image data is read, and the FPN data is furtherread again. Back to the idling operation, the still image radiographingis performed on the second piece of data.

In part (a) of FIG. 16, the “IDLE” signal is switched to the pointbefore the irradiation of X-rays. In part (b) of FIG. 16, the “IDLE”signal is switched to the point after the irradiation, that is, thepoint immediately before the reading operation. Either case is accepted,but the heat generation can be more efficiently reduced in part (b) ofFIG. 16.

In FIG. 14, only one channel is expressed for convenience of the layouton the sheet, but it is obvious that a multi-channel configuration asillustrated in FIG. 13 can be accepted.

The flat panel X-ray detector 11 can perform moving image radiographingand still image radiographing in the connecting state radiographing, andthe idling drive and the still image radiographing in the non-connectingstate radiographing.

(Fifth Mode for Embodying the Present Invention)

FIG. 17 is a timing chart illustrating the operation according to thepresent mode for embodying the present invention, and shows a timingduring non-connecting state radiographing. Although FIG. 16 illustratesonly the example of still image radiographing, FIG. 17 illustratescombination radiographing of the fluoroscopic radiographing and thestill image radiographing. In the fluoroscopic radiographing, a BIASterminal is placed in the “Lo” (off) state, to reduce the powerconsumption of the operational amplifier, thereby suppressing the heatgeneration. However, in this case, the BIAS terminal is somewhatdisadvantageous in respect of speed as compared with the BIAS terminalin the “Hi” state. Therefore, high-speed fluoroscopic radiographingcannot be performed as compared with the case of the BIAS terminal inthe “Lo” state. When there is a request for the still imageradiographing, the X-rays for still images are emitted, a readingoperation for one frame of still images is performed, and the readingoperation of the FPN is further performed. In FIG. 17, the BIAS terminalis placed in the “Hi” state in this period.

The random noise of a transistor depends on the bias current passingthrough the differential transistor pair at the input stage of anoperational amplifier. Generally, by passing a strong current, theconductance of the differential transistor pair at the input unit isreduced, thereby suppressing the noise. In the present mode forembodying the present invention, since radiographed still image is usedfor a diagnosis, the BIAS terminal is placed in the “Hi” state in thestill image radiographing.

However, when the amount of X-ray irradiation can be set large, or whenthe S/N ratio is not so strict, it is not necessary to strictly set theBIAS terminal in the “Hi” state. That is, the selection can be madedepending on the purpose of radiographing and diagnosis.

(Sixth Mode for Embodying the Present Invention)

FIG. 18 illustrates the outline of the X-ray imaging apparatus accordingto the sixth mode for embodying the present invention. It indicates thestructure of the C arm and the X-ray detector. The apparatus includes aphosphor 901, a heat dissipation plate 902, a heat pipe 903, a readcircuit 904, a heat exchange 905, a C arm 906, a signal-power supplycable 907, a heat pipe 908, a heat dissipation plate 909, a heatconductive sheet 910, a connector 911, a fixing hook 912, a flat panelX-ray detector 913, a support substrate 914, a two-dimensional sensor915, a system substrate 916, an extension cable 917, and a connectionstate detection unit 990.

The flat panel X-ray detector 913 according to the present mode forembodying the present invention is a two-dimensional sensor having thecircuit configuration shown in FIGS. 3, 11, and 12, and on the opticalincident plane the phosphor 901 is provided for converting X-rays intovisible light. Reference numeral 904 designates a read circuit. No drivecircuit is illustrated in FIG. 9. The components are connected to thesupport substrate 914.

Fixed to the support substrate 914 are the power supply control unit forcontrolling and supplying power such as an AD converter, a drivingcircuit unit (not shown in the attached drawings), a timing generationunit, a radiation detection circuit, a driving circuit unit, a read-outcircuit unit, etc. and a system substrate such as an arithmeticoperation unit provided with memory, a CPU, etc. The AD converter A/Dconverts a signal output from the read-out circuit unit. The timinggeneration unit assigns timing to the read circuit. There is one systemsubstrate 916 illustrated in FIG. 18, but a plurality of substrates canbe provided.

In the present mode for embodying the present invention, the flat panelX-ray detector 913 is provided with the heat dissipation plate 902. Theheat pipe 903 is connected to the heat dissipation plate 902 so that theheat generated by the read circuit 904 and the like is transmitted.

The C arm 906 is provided with the heat dissipation plate 909 and theheat conductive sheet 910 as with the above-mentioned flat panel X-raydetector 913. In the state in which the C arm 906 and the flat panelX-ray detector 913 are combined, the heat dissipation plate 902 of theflat panel X-ray detector 913 is thermally connected to the heatdissipation plate 909 of the C arm 906 through the heat conductive sheet910.

The C arm 906 is provided with the heat pipe 908 and the heat exchange905 for externally dissipating the heat of the heat dissipation plate909, and the heat transmitted from inside the flat panel X-ray detector913 can be radiated externally. The flat panel X-ray detector 913 hasheat dissipation transmission unit for transmitting and dissipating thegenerated heat to the C arm 906 when the detector is connected to the Carm 906.

The heat pipe 908 is generally referred to as a heat conductive systemon the basis of a reciprocal change between vaporization andliquefaction of a liquid sealed inside and a capillary phenomenon. Thethermal conductivity of the heat pipe 908 is considerably high, and theheat can be efficiently transmitted.

The heat pipe 908 has a high degree of freedom, has no moving portion,and requires no maintenance. Therefore, it is applicable to a devicerequiring high reliability such as medical equipment.

The materials of the heat dissipation plates 902 and 909 in the presentmode for embodying the present invention can be metal of high thermalconductivity such as copper, aluminum, etc.

The heat conductive sheet 910 is a sheet of silicone rubber and anacrylic rubber of high thermal conductivity. In connecting heatdiffusion plates of metal, the air layer between the plates prevents theheat from being efficiently conducted. However, the heat conductivesheet 910 avoids the defect. The heat conductive sheet 910 is fixed tothe heat dissipation plate 909 on the C arm 906.

The electrical connection between the C arm 906 and the flat panel X-raydetector 913 according to the present mode for embodying the presentinvention is made simultaneously when the flat panel X-ray detector 913is fixed to the C arm 906.

The electrical connection between the radiographing system including theC arm 906 and the flat panel X-ray detector 913 is made by the connector911. Necessary power supply and electrical signal for driving the flatpanel X-ray detector 913 are supplied from the C arm 906 through theconnector 911, and the image data and the status signal of the systemare output from the flat panel X-ray detector 913 to the C arm 906.

Part (b) of FIG. 18 illustrates the state in which the flat panel X-raydetector 913 is separated from the C arm 906. When the flat panel X-raydetector 913 is separated from the C arm 906, the radiographing usingthe flat panel X-ray detector 913 can be performed by connecting theextension cable 917 to the connector 911.

The connection state detection unit (connection detection unit) 990 inFIG. 18 detects the time (non-connecting state) when the flat panelX-ray detector 913 is connected to the C arm 906 and when it is removedfrom the C arm 906. Whether it is a connected state or a non-connectedstate is detected, and according to a resultant signal, the heatgeneration quantity of the X-ray imaging unit is differentiated.

FIG. 22 illustrates the outline of detecting the connected state by theconnection state detection unit 990 provided for the C arm 906, andcontrolling the X-ray imaging unit according to the control signal.

According to the control signal from the connection state detection unit990, a feedback is applied to the arithmetic operation unit 106 in FIGS.1 and 2, and according to the control signal from the arithmeticoperation unit 106 to the power supply control unit 104, the voltagesVs, Vcom, Vdd, Vref1, etc. are controlled, and the heat generationquantity is controlled.

Additionally, according to the control signal from the connection statedetection unit 990, in FIG. 8, the current source 801 is controlled,thereby changing the heat generation quantity.

Furthermore, according to the control signal from the connection statedetection unit 990, the heat generation quantity can be changed bycontrolling the switch 1011 as illustrated in FIGS. 11 and 13.

According to the control signal from the connection state detection unit990, the heat generation quantity can be changed by changing the state(enabled/disabled) of each of the read circuit and the drive circuit asillustrated in FIG. 12. Although not illustrated in FIG. 12, the methodof selecting the states can be easily attained by fully using thepresent digital technology.

Also according to the control signal from the connection state detectionunit 990, as illustrated in FIGS. 15, 16, and 17, the heat generationquantity can be changed by changing the IDLE signal and the BIAS signal.Although not illustrated in the attached drawings, the method ofgenerating the IDLE signal and the BIAS signal can be easily attained byfully using the present digital technology.

FIGS. 21A and 21B illustrate examples of the connection state detectionunit 990. FIG. 21A illustrates an electric circuit, and FIG. 21Billustrates the mechanical concept.

A light emission diode (LED) 991 is turned on when the light from thelight emission diode 991 is emitted to the base portion (light receivingportion) of a phototransistor 992, and the control signal enters the“Lo” level. When the light of the light emission diode 991 is notemitted to the light receiving portion of the phototransistor 992, thediode is turned off, and the control signal enters the “Hi” state.

A member 993 has an embedded electric circuit illustrated by FIG. 21A.The light of the LED that has passed a window 995 is input to thephototransistor unit (not illustrated in FIGS. 21A and 21B) through thewindow (not illustrated in FIGS. 21A and 21B) provided in the oppositeportion. A shading member 994 is a shading member for cutting off thelight between the LED and the phototransistor when the X-ray imagingunit is connected to the C arm 906, and allowing the light of the LED tobe emitted to the phototransistor when the C arm is removed, that is,when it is not connected. In FIGS. 21A and 21B, the control signal is inthe “Hi” state when the C arm is connected, and in the “Lo” state whenthe C arm is disconnected. FIG. 21B is referred to as aphotointerrupter. The wavelength of the light of the light emissiondiode 991 can be infrared or visible light as long as the light isshaded from the surrounding light. However, when the surrounding light(fluorescent light) enters, it is desired that an infrared LED is used.

In FIG. 18, the C arm 906 is connected to the flat panel X-ray detector913 through the extension cable 917. However, if there is a connectorhaving the same function as the connector 911, a connection can be madeto the connector.

For example, a connection can be made to the connector of the mobileX-ray generation apparatus 13 provided with wheels as illustrated inFIG. 20.

The mechanical connection between the C arm 906 and the flat panel X-raydetector 913 is made by the fixing hook 912. They are fixed with hook inthe groove on the side of the housing of the flat panel X-ray detector913.

In the non-connecting state radiographing, a cable can interfere withthe radiographing and a hand or a foot can touch and destroy the flatpanel X-ray detector 913 in the act of radiographing. Therefore, ano-cable system (cable less) is desired. A drive signal input to theflat panel X-ray detector 913 can be externally controlled by wirelesscommunication by providing a wireless interface and an antenna in theflat panel X-ray detector 913. Otherwise, wireless communications can bestopped, and a timing generation unit and a control unit can be providedin the flat panel X-ray detector 913. The digital signal with imageinformation from the flat panel X-ray detector 913 can also be used inthe wireless communication, and a storage unit capable of accumulatingradiographing data on the flat panel X-ray detector 913 and easilyattached and removed such as USB memory, an MO disk, a hard disk, etc.can be provided.

In the non-connecting state radiographing, to attain a cableless system,it is necessary to provide a power supply (battery) for the flat panelX-ray detector 913 at the inside of the flat panel X-ray detector 913.The connecting state radiographing performed when the C arm 906 isconnected uses the power supply of the X-ray radiographing apparatus.The non-connecting state radiographing is driven by a battery providedin the flat panel X-ray detector 913. It is desired that the battery hasa large capacity and can be charged. However, a larger capacity has theproblem of a heavier system. The flat panel X-ray detector 913 requestedin the non-connecting state radiographing is a light and easily portableunit. Therefore, a necessary battery has to be smaller in capacity to acertain extent. According to the present mode for embodying the presentinvention, these conditions can be satisfied. That is, the present modefor embodying the present invention for driving the non-connecting stateradiographing with suppressed heat generation improves the batterysystem required in realizing a cableless system.

The modes for embodying the present invention have been described above,and the terms are defined as follows. The fluoroscopic radiographing issynonymous with moving image radiographing, and an observer cancontinuously observe X-ray images in real time through a monitor and thelike, or the X-ray images can be temporarily stored on a storage mediumas digital data, then separately regenerated, and observed by a monitor.All or a part of the fluoroscopic radiograph image data stored on thestorage medium can be printed on paper or film, and can be observed as aplurality of still images.

Similarly, the still image radiographing is performed, that is, theimages can be observed as is by a monitor, or observed after stored inmemory, whichever can be optionally selected.

The flat panel X-ray detector 913 has the structure of the radiationdetection substrate 101, the drive circuit unit 103, the read-outcircuit unit 102, and the AD conversion unit 105 adhered to the supportplate 914 or fixed by a screw. The structure is covered with a coveringmember for covering the entire structure.

The radiation incident plane of the covering member is made from thematerial mainly composed by carbon, and the portions other than theradiation incident plane are made of any of magnesium, aluminum,stainless steel, and plastic. The support plate is made of any ofmagnesium, aluminum, stainless steel, and plastic.

The flat panel X-ray detector 913 is provided with at least one handleportion for portability. The flat panel X-ray detector 913 is providedwith a battery, and power is supplied from the power supply wiring viathe C arm 906 during the connecting state radiographing. In thenon-connecting state radiographing, power is supplied from the battery.The battery is designed to be easily removed.

The flat panel X-ray detector 913 is provided with memory, outputs datathrough electric wiring for data transfer via the C arm 906 in theconnecting state radiographing. In the connecting state radiographing,data is accumulated in the memory. The memory can be easily removed.During the connecting state radiographing, the radiographing can beperformed with electric wiring connected via the C arm 906. During thenon-connecting state radiographing, the radiographing can be performedwith the C arm 906 completely disconnected.

The radiation detection element PD includes a wavelength conversionelement for converting radiation into visible light, an optoelectronicconversion element for receiving visible light and converting it into anelectrical signal. The wavelength conversion element is configuredmainly by at least one of Gd₂O₃, Gd₂O₂S, and CsI. The optoelectronicconversion element is configured mainly by amorphous silicon.

The radiation detection element PD is mainly made of any of selenium(Se), gallium arsenide (GaAs), silver iodide (HgI2), lead iodide (PbI2),zinc sulfide (ZnS), zinc selenium (ZnSe), cadmium tellurium (CdTe), leadtellurium (ZnTe), and combined crystal of tellurium, lead, and cadmium(ZnCdTe), and can be a conversion from radiation directly into electriccharge without a phosphor.

In FIGS. 19 and 22, the C arm 16, to which the flat panel X-ray detector11 and the radiation source 12 are connected, is connected to a wagonprovided with wheels 25. The wagon includes the system controllers 20and 21 for controlling the radiation source 12 and the flat panel X-raydetector 11, an image processing unit, and a data storage unit, andfurthermore the power supply of a radiation source, a power supply of aradiation detection circuit unit, and an heat exchanger for dissipatingthe heat of the radiation detection circuit unit and the radiationsource. Provided outside the wagon is at least one monitor 22 capable ofobserving an image radiographed by the flat panel X-ray detector 11. Atthe connection point between the wagon and the C arm 16, the C arm 16has the mechanism of allowing back and forth, right and left, up anddown movement and rotation.

A convenient X-ray imaging apparatus can be provided as a device capableof performing not only the fluoroscopic radiographing performed in thestate in which the C arm is connected and the radiographing of a stillimage, but also the radiographing performed in the state in which the Carm is disconnected. If the radiographing can be performed with theX-ray detector removed from the C arm, not only the X-ray sourceconnected to the C arm, but also the X-rays separately provided in theradiographing room can be used. Therefore, not only the convenience, butalso the image quality can be improved. During the non-connecting stateradiographing, it is advantageous in driving using a battery because thedrive is performed with suppressed power consumption. Furthermore, inthe non-connecting state radiographing, a cableless cassette as well asa film cassette can be used.

The above-mentioned modes for embodying the present invention indicatepractical examples of embodying the present invention, and the technicalscope of the present invention is not restricted. That is, the presentinvention can be embodied in variations within the technical concepts,gist, and characteristics of the present invention.

Furthermore, the present invention includes the embodiment realized byoperating various devices according to the program stored in a computer(CPU or MPU) of the system or the device to realize the functions of theabove-mentioned modes for embodying the present invention, and operatingthe computer in a device or a system connected to the various devices toprovide a program code of software for realizing the function of themodes for embodying the present invention from the storage medium orthrough a transmission medium such as the Internet and the like.

In this case, the program code itself of the software realizes thefunctions of the modes for embodying the present invention, and theprogram code itself, the unit for supplying the program code to thecomputer, for example, a storage medium storing the program codeconfigure the present invention. A storage medium storing the programcode can be, for example, a flexible disk, a hard disk, an optical disk,an magneto optical disk, CD-ROM, magnetic tape, a non-volatile memorycard, ROM, etc.

The modes for embodying the present invention also include not only thecase in which the functions described by referring to theabove-mentioned modes for embodying the present invention are realizedby executing the provided program code by the computer, but also thecase in which the functions described by referring to theabove-mentioned modes for embodying the present invention with the OS(operating system) or other application software operating in thecomputer including the program code are realized.

Furthermore, the present invention also includes the case in which thefunctions of the modes for embodying the present invention are realizedby the process of storing a supplied program code in memory in a featureexpansion board of a computer and a feature expansion unit connected tothe computer, and performing all or a part of the actual process by theCPU and the like provided in the feature expansion board and the featureexpansion unit according to the instruction of the program code.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

1. A radiation imaging apparatus, comprising; a flat panel detectorincluding picture elements arranged in a matrix of rows and columns on asubstrate, each picture element having a conversion element forconverting radiation into an electrical signal, a signal wiringconnected to the picture elements in a column, and a read-out circuitunit connected to the signal wiring; a holding unit for holding saidflat panel detector; and a control unit for controlling said flat paneldetector, wherein said flat panel detector can be connected to anddisconnected from said holding unit, and wherein connecting stateradiographing can be performed with the flat panel detector connected tothe holding unit, and non-connecting state radiographing can beperformed with the flat panel detector disconnected from the holdingunit, and wherein said control unit controls said flat panel detector sothat a power supply voltage applied to said read-out circuit unit in thenon-connecting state radiographing is lower than that of applied to saidread-out circuit unit in the connecting state radiographing, and so thata change in characteristics of said read-out circuit unit due to achange of the power supply voltage is compensated for.
 2. The radiationimaging apparatus according to claim 1, wherein said read-out circuitunit includes integrating circuit which has an operational amplifier anda capacitor for defining a gain of the operational amplifier, and saidcontrol unit controls the power supply voltage and the gain in theconnecting state radiographing and the non-connecting stateradiographing.
 3. The radiation imaging apparatus according to claim 1,wherein the flat panel detector comprises a heat dissipationtransmission unit for transmitting generated heat to the holding unitand dissipating heat in a state in which the detector is connected tothe holding unit.
 4. The radiation imaging apparatus according to claim1, wherein the flat panel detector can perform moving imageradiographing and still image radiographing in the connecting stateradiographing, and can perform idling drive and still-imageradiographing in the non-connecting state radiographing.
 5. Theradiation imaging apparatus according to claim 1, further comprising aconnection detector for detecting whether or not said flat paneldetector is connected to said holding unit, wherein said control unitcontrols said flat panel detector according to result of detection bythe connection detector.